As more efficient communication systems have developed, a number of communication standards having different operating frequencies and modulation methods have been adopted. Because various standards imply the parallel composition of several independent signal paths, the multi standards consequently increase the size and cost of circuits. If reconfigurable circuit designs are possible, then the cost and the size of parallel circuits can decrease with the aid of those circuits. Therefore, recently, the design of adaptive radio frequency (RF) circuits has been thoroughly investigated.
RF circuits can be typically categorized into two parts, a receiver and a transmitter. Of the two, the receiver path has already been successfully implemented with tunability while the transmitter path has not. The transmitter path implementation, especially a power amplifier, is challenging due to the large signal operation that requires tunable capacitors or inductors that should maintain their performance up to high power. If these tunable components for high power application are available, then one can improve significantly the performance of the transmitter, especially power amplifier.